Process for the preparation of adiponitrile by dimerization of acrylonitrile



July 6, 1965 A. KA-rcHALsKYV ETAL 3,193,574

PROCESS FOR THEPREPARATION OF ADIPONITRILE BY DIMERIZATION OF ACRYLONITRILE Filed May 2A. 1961 United States Patent C 3,193,574 PRCESS FOR THE PREPARATIDN F ADIPO- NTRILE BY DIMERIZATION 0F ACRYLO- NITRILE Aharon Katchalslry, 18 Dubnov Str., Tel Aviv, Israel; David Vofsi, Neve Weizmann, Rehovoth, Israel; and Jacob Israel Padova, 46 S. Stanworth Drive, Princeton, NJ.

Filed May 2, 1961, Ser. No. 107,232 Claims priority, appiication Israel, May 8, 1960, 13,842, 13,844 11 Claims. (Cl. 26046S.8)

It is an object of the present invention to provide a process for the preparation of adiponitrile by the dimerization of acrylonitrile. i

It has already been suggested to prepare adiponitrile froml acrylonitrile in an acidic aqueous reacti-on system containing a small proportion of an alkali-metal amalgam, e.g. sodium or potassium amalgam, as a promoter. It is also known that for a steady performance of this process the proportion of the alkali metal in the amalgam is of decisive importance. It has, moreover, been suggested to prepare the amalgam by electrolysis concurrently with the dimerization of the adiponitrile in an electrolytic cell separate from the reactor and connected to the latter by conduits through which fresh amalgam is supplied to the reaction mixture, and mercury is continuously returned tothe electrolytic cell, while the dimerization pro- For the sake of brevity this process will be referred to herein as indirect electrolysis, it being understood that the electrolysis that takes place in the process produces merely the alkali metal amalgam required for -the dimerization of the acrylonitrile but does not conyield, even if the rate of supply of amalgam to the reaction system is carefully adjusted. Besides Vthe desired dimer, various proportions of undesired polymers and other by-products are formed. With low amperages of the'current passing through the electrolytic cell, i.e. with low proportions of alkali metal content of the amalgam currently supplied to the reaction mixture, polymers are produced predominantly. As the alkali metal content of the amalgam rises, so does the proportion of dimer formedthough not above about 20%-vvhile the formation of polymers drops-though not below about 46%- these yield percentages being by weight of the amount of acrylonitrile used as starting material.

It has now surprisingly been found that by the use of a reaction mixture, containing certain additives, the yield of dimer can be increased considerably and the formation of polymers and other by-products can be reduced drastically. These additives have presumably a catalytic action and will therefore be referred to hereinafter as catalysts for short.

The catalysts to be used in accordance with this invention are organic compounds that are polymerization inhibitors and belong to one of the following groups: quinones, polyphenols, aromatic amines, aminophenols, aminoquinones and quinonimines. Suitable catalysts are, for example, benzoquinone, anthraquinone, isatin, hydroquinone, pyrogallol, alpha-naphthylamine, beta-naphthylamine, alpha-amino anthroquinone, beta-amino anthraquinone. Mixtures of these compounds may be used.

The action of the catalysts according to the invention can be enhanced bythe addition to the reaction mixture of promotors, which are salts of certain metals, especially transition metals, such as those containing ferrous, ferric, cobalt or nickel ions.

ice

The yield of adiponitrile can be further increased if acetone is admixed with the reaction mixture, though in this case some more polymer is also formed.

For the acidulation of the aqueous reaction mixture, any of the conventional mineral acids may be used, e.g. hydrochloric, hydrobromic, sulfuric or phosphoric acid; of these acids, hydrochloric acid is especially preferred. No exact degree of acidity need be prescribed, as the optimal working conditions can easily be found by experiment for any particular set of circumstances under which the process according to the invention is to be performed. In the case of hydrochloric acid, however, a concentration of 1% by weight of HCl in the react-ion mixture can be said to be a practical lower limit for satisfactory performance. Upper limits will be dictated by extraneous considerations, e.g. the desire not to use more acid than is required for the economic performance of the process, not to make the reaction mixture more corrosive than is necessary, and to avoid the crystallization from the reaction mixture of salts of the acid concerned.

The optimal proportion .of alkali metal in the amalgam fed to the reaction mixture is comprised within a rather wide range. In the case of potassium this is about 0.001 to 0.1%, with a preferred range from 0.01 to 0.05%. In the case of other alkali metals the proportion will be calculated correspondingly.

The process according to the invention can be carried out conveniently at temperatures from 0 to 40 C., preferably in the range from 15 to 25 C.

The process according to the invention can be carried out in an apparatus of the type shown diagrammatically in the accompanying drawing.

This apparatus comprises an electrolytic cell 1 and a reactor 3. These two vessels are interconnected by a feed pipe 8.which includes a feed pump 15. The suction end 16 of pipe 8 extends down to nearly the bottom of the cell 1; the delivery end of pipe 8 opens into the top part of the reactor. The two vessels are further interconnected by a return pipe 2 substantially at bottom level. A cathode 14 is disposed in the bottom part of the electrolytic cell 1 within a layer 4 of mercury. An anode 13 is located higher up in the cell 1 within an aqueous layer 5 constituted by the aqueous solution of an electrolyzable compound of the alkali metal to be converted into an amalgam. Both electrodes are connected to a D.C. source symbolized as a battery 12.

The reactor 3 is fitted with a double stirrer comprising, on a vertical shaft 6, a lower set of blades dipping into a bottom layer 4 of mercury, and an upper set of blades located within the aqueous reaction liquid 7. The mercury layer 4 in the reactor communicates through pipe 2 with the mercury layer 4 in the cell 1. The rcactor is further fitted with a dropping funnel 9, a reux condenser 11 and a thermometer 10.

This apparatus is referred to in the following examples which illustrate the invention but to which the latter is not limited. The indications of yield percentages in the examples are calculated on the weight of the acrylonitrile, used as starting material.

Example 1 A total quantity of about 1000 ml. of mercury was introduced into the two vessels 1 and 3; the surface area of the mercury was about 200 cm.2 in the cell 1 and about 250 cm.2 in the reactor 3. On top of the mercury layer 4 the cell 1 contained about 1000 g. of a 40% -by-weight aqueous potassium hydroxide solution 5. A layer 7 of a solution of 42.6 g. of acrylonitrile in 366 g. of 20%-by-weight hydrochloric acid was introduced into the reactor 3 on top of the mercury. The dropping funnel 9 contained about ml. of 36%-by-weight hydrochloric acid.

400 mg. of hydroquinone was added as a catalyst to the acrylonitrile solution in the reactor 3 while the stirrer 6 and pump 15 were actuated and a current of about 9 amps. Was passed for about 6 hours through the cell 1 at a temperature `of about 25 C. During this time a total of about 180 nil. of the 36%-by-Weight hydrochloric acid was dropped at a steady rate from funnel 9 into the reactor 3.

The electrolysis going on in the cell 1 produced potassium amalgam at the cathode, and this was continuously transferred to the reactor by the pump 15. With the amperage and the concentration of the potassium hydroxide solution indicated above, the proportion of potassium metal in the amalgam being supplied to the reactor 3 remained in the range between 0.01 and 0.05%. Amalgam was decomposed in the reactor, and depleted amalgam is continuously returned through pipe 2 to the cell 1. Hydrogen evolved in the reactor 3 escaped through the condenser ill where any volatile substances carried off with the hydrogen were refiuxed.

At the end of the six hours aforesaid the current was discontinued, the organic substances were extracted with chloroform from the aqueous reaction mixture in the reactor 3, and the chloroform extract was separated and then fractionated by distillation. The first fraction was distilled under atmospheric pressure, the subsequent fractions under reduced pressure. The fractions obtained were weighed and identified. The yield consisted of 40.4 percent of adiponitrile and 7.9 percent of propionitrile.

Example 2 A run was carried out similarly as described in Example 1 but in addition to 400 mg. of hydroquinone, 600 mg. of CoClZ were added as a promoter to the reaction mixture for enhancing the action of the catalyst'.

The yield consisted of 42.7 percent of adiponitrile and 5.6 percent of a polymeric substance.

Example 3 A run was carried out similarly as described in Example l but the reaction mixture contained 600 mg. of anthraquinone as a catalyst, 170 mg. of CoClz a-s a promoter, and 8.5 g. of acetone.

The yield of adiponitrile Was 68.5 percent besides traces of polymeric substance.

Example 4 A run was carried out similarly as described in Example l but the reaction mixture contained 425 mg. of anthraquinone as a catalyst, 210 mg. of FeCl2 as a promoter, and 15.5 g. of acetone.

The yield consisted of 70.4% of adiponitrile and 18% of polymeric substance.

Example 5 A run was carried out similarly as described in Example 1 but the reaction mixture contained 600 mg. of isatin as a catalyst, 170 mg. of CoCl2 as a promoter, and 15.5 g. of acetone.

The yield consisted of 73.5% of adiponitrile and 14.1% of a polymeric substance.

Example 6 A run was carried out similarly as described in Example l but the reaction mixture contained 425 mg. of amino anthraquinone as a catalyst, 210 mg. of CoCl2 as a promoter, and 15.5 g. of acetone.

The yield consisted of 75% of adiponitrile besides traces of a polymeric substance.

ln these examples the process according to the invention has been describde as a batch process. It can instead be performed in a continuous manner.

What we claim is:

1. A process yfor the production of adiponitrile, com

prising dirnerizin g acrylonitrile in an aqueous reaction mixture maintained at temperatures of from 0 to 40 C., said reaction mixture containing a mineral acid, an alkali metal amalgam containing from 0.001 to 0.1% alkali metal and an organic additive selected from the group consisting of benzoquinone, anthraquinone, isatin, hydroquinone, pyrogallol, alpha-naphthylamine, beta-naphthylamine, alphaamino anthraquinone, beta-amino anthraquinone, and mixtures thereof.

2. The process as defined lin claim additive is benzoquinone.

3. The process as defined in additive is anthraquinone.

4. The process as defined in additive is isatin.

5. The process as defined in additive is hydroquinone.

6. The process as defined in additive is pyrogallol.

7. The process as defined in additive is alpha-naphthylamine.

8. The process as defined `in additive is beta-naphthylamine.

9. The process as defined in claim additive is alpha-aminoanth-raquinone.

v10. The process as defined in claim additive is beta-aminoanthraquinone.

11. A process for the production `of adiponitrile by the dimerization of .acrylonitrile in an aqueous acidic reaction mix-ture containing an alkali metal amalgam which comprises:

(a) charging Lacrylonitrile lin an aqueous `reaction mixture acidified with a mineral acid selected from the group consisting of hydrochloric, hydrobromic, sulfuric `and phosphoric acids, and containing an organic additive selected from the group consisting of benzoquinone, anthraquinone, isatin, hydroquinone, pyrogallol, alpha-naphthylamine, beta-naphthylamine, alpha-amino anthraquinone, beta-amino anthraquinone, and mixtures thereof, to a first reaction zone;

(b) electrolyzing a mixture of an alkali metal and mercury in a second reaction zone to produce an alkali metal amalgam containing from 0.001% to 0.1% of said alkali metal;

(c) continuously feeding said alkali metal amalgam to the aqueous reaction mixture in the first reaction zone;

(d) maintaining said Areact-ion mixture in said rst reaction zone at temperatures of from 0 to 40 C. to effect dimerization of the acrylonitrile therein to adiponitrile; and

(e) continuously removing mercury from said first reaction zone .and recycling the same to said second reaction zone for the production of additional amounts of said alkali methyl amalgam therefrom.

`l, in which said claim in which said claim `in which said claim in which said claim in which said claim in which said claim in which said which said which said References Cited by the Examiner UNITED STATES PATENTS 2,346,425 4/ 44 Kirkpatrick.

2,607,795 8/52 Stehman 260-465.9 2,768,962 10/56 Krimm 260-464 2,803,643 8/ 57 Halliwell 260-465-8 OTHER REFERENCES CHARLES B. PARKER, Primary Examiner. 

1. A PROCESS FOR THE PRODUCTION OF ADIPONITRILE, COMPRISING DIMERIZING ACRYLONITRILE IN AN AQUEOUS REACTION MIXTURE MAINTAINED AT TEMPERATURES OF FROM 0* TO 40*C., SAID REACTION MIXTURE CONTAINING A MINERAL ACID, AN ALKALI METAL AMALGAM CONTAINING FROM 0.001 TO 0.1% ALKALI METAL AND AN ORGANIC ADDITIVE SELECTED FROM THE GROUP CONSISTING OF BENZOQUINONE, ANTHRAQUINONE, ISATIN, HYDROQUINONE, PYROGALLOL, ALPHA-NAPHTHYLAMINE, BETA-NAPHTHYLAMINE, ALPHAAMINO ANTHRAQUINONE, BETA-AMINO ANTHRAQUINONE, AND MIXTURES THEREOF. 